We are investigating the genetic control of serum IgE levels, and the relationship between the genetic control of IgE and the inheritance of allergy. Preliminary studies suggest that a simple genetic system controls basal IgE levels in man, possibly similar to the genetic control of the reagin response observed in mice. These studies are also in quantitative agreement with the inheritance of atopy in man. The objective of this study is to further the genetics of IgE, and to study the postpartum development of IgE relative to other immunoglobulins. Family studies will be extended, using quantitative measurements of serum IgE levels. Additionally we will measure the ratio of IgE antibody to total antibody produced in response to a purified antigen, to determine the characteristics of the IgE response and to determine if the IgE response is proportional to the serum IgE level. The relationship of the development of the serum immunoglobulins, and specific antibody response in IgG, IgM, IgA and IgE will be studied in infants in order to characterize the primary IgE response and the temporal and quantitative relationships among the immunogloblin classes during the response. This study will be conducted with infants born of parents having atopy and high IgE levels, and with infants born of parents having no atopy and low IgE levels. Ultimately we expect to develop criteria which prospectively distinguish infants at risk of childhood onset allergy. These criteria will be tested for their utility in a larger population, with the intent of making possible the appropriate environmental control for postponement, amelioration or prevention of predicted allergic disease.